1. Field of the Invention
The present invention relates to an ink jet printer. The present invention further relates to a method for controlling an ink jet printer, and a computer program product for an ink jet printer. The ink jet printer of the present invention includes all devices for printing words, images, etc. by discharging ink towards a print medium. For example, the ink jet printer of the present invention includes copying machines, fax machines, etc.
2. Description of the Related Art
An ink jet printer has an ink jet head for printing on a print medium by means of discharging ink. Some ink jet heads have a plurality of units. Each unit has a nozzle for discharging ink, a pressure chamber communicating with the nozzle, and a piezoelectric element facing the pressure chamber. When the piezoelectric element is deformed toward a pressure chamber, capacity of the pressure chamber decreases. Then the ink within the pressure chamber is pressurized, and the pressurized ink is discharged from the nozzle.
Selection of the piezoelectric element of which voltage is to be changed causes a selection of the pressure chamber within which the pressure is to be changed. The selection of the pressure chamber within which the pressure is to be changed causes a selection of the nozzle from which ink is to be discharged. In the ink jet head with the above configuration, ink can be discharged from a desired nozzle by changing the voltage of a selected piezoelectric element. An ink jet printer having this type of ink jet head is taught in U.S. Pat. No. 5,402,159.
In the above type of ink jet head, the piezoelectric elements are disposed in a matrix shape within a predetermined plane. Here, the piezoelectric elements aligned in a first direction in the predetermined plane will be termed an element line. Each element line is aligned in a second direction which is different from the first direction.
Each piezoelectric element faces a corresponding pressure chamber. Consequently, the pressure chambers are also disposed in a matrix shape. Here, the pressure chambers aligned in the first direction will be termed a pressure chamber line. Each pressure chamber line is aligned in the second direction.
The nozzles are also disposed in a matrix shape. Here, the nozzles aligned in the first direction will be termed a nozzle line. Each nozzle line is aligned in the second direction. The nozzles that are disposed in the matrix shape are mutually offset in the first direction. The units having the piezoelectric elements that are included in the same element line have the nozzles that are included in the same nozzle line.
FIG. 20 is a simplified view showing an example of an arrangement of the element lines and the nozzle lines. Four element lines X1 to X4 are formed in FIG. 20. One element line consists of four piezoelectric elements aligned in the first direction. Sixteen piezoelectric elements are disposed in a matrix shape. One nozzle corresponds to one piezoelectric element. Four nozzle lines Y1 to Y4 are formed. Each of the sixteen nozzles is mutually offset in the first direction.
In this example, a print medium (for example, a print sheet) is moved at a uniform speed in the second direction. If a straight line Z1 and a straight line Z2 are to be printed on the print medium, the following operation is performed. The distance between the straight line Z1 and the straight line Z2 is equal to the distance between two adjacent nozzle lines (for example, Y1 and Y2). The print medium is moved in the second direction firm the state shown in FIG. 20. When the nozzle line Y1 is facing the position where the straight line Z1 is to be printed, all of the piezoelectric elements in the element line X1 are simultaneously deformed. Ink is thus simultaneously discharged from the four nozzles in the nozzle line Y1. Next, when the nozzle line Y2 is facing the position where the straight line Z1 is to be printed (when the nozzle line Y1 is facing the position where the straight line Z2 is to be printed), the piezoelectric elements in the element line X1 and the piezoelectric elements in the element line X2 are simultaneously deformed. Ink is thus simultaneously discharged from the nozzles in the nozzle line Y1 and the nozzles in the nozzle line Y2. Next, when the nozzle line Y3 is facing the position where the straight line Z1 is to be printed, the piezoelectric elements in the element line X2 and the piezoelectric elements in the element line X3 are simultaneously deformed. Next, when the nozzle line Y4 is facing the position where the straight line Z1 is to be printed, the piezoelectric elements in the element line X3 ad the piezoelectric elements in the element line X4 are simultaneously deformed. Finally, when the nozzle line Y4 is facing the position where the straight line Z2 is to be printed, the piezoelectric elements in the element line X4 are simultaneously deformed. The two straight lines Z1 and Z2 are thus printed on the print medium.
The piezoelectric elements may be formed from a common piezoelectric sheet that extends across the plurality of pressure chambers. The following phenomenon may occur if this type of common piezoelectric sheet is used. When only one of two adjacent piezoelectric elements is deformed, the other adjacent piezoelectric element may also be deformed. In the present specification, the phenomenon in which the deformation of one piezoelectric element affects the degree of deformation of a piezoelectric element adjacent thereto is termed a structural cross-talk phenomenon. When there is deformation of a piezoelectric element in which deformation was not desired, ink may be discharged from an untended nozzle, or ink may be discharged with an unintended timing. In this case, satisfactory printing results cannot be achieved.
The structural cross-talk phenomenon has an effect not only in the case where only one of two adjacent piezoelectric elements is deformed, but also has an effect in the following case. As in the aforementioned example of FIG. 20, ink may be discharged simultaneously from two adjacent nozzles in the ink jet printer. The two adjacent piezoelectric elements may be simultaneously deformed in the same direction. In this case, one of the two adjacent piezoelectric elements may have a smaller degree of deformation than in the case where only one of the two adjacent piezoelectric elements is deformed. When the degree of deformation of the piezoelectric element changes, there is a change in the amount of pressure that is increased or decreased in the pressure chamber facing the piezoelectric element. When the amount of pressure that is increased or deceased in the pressure chamber changes, there is a change in the amount of ink discharged from the nozzle that communicates with the pressure chamber. When the amount of ink discharged from the nozzle changes, the amount of ink adhering to the print medium is unstable.
Moreover, the structural crosstalk phenomenon also occurs in the case where the aforementioned common piezoelectric sheet is not used. The structural cross-talk phenomenon may occur even in the case where the piezoelectric elements are formed from individual piezoelectric sheets. Specifically, when a common vibration plate is formed between the piezoelectric elements and the pressure chambers, the deformation of a certain vibration region corresponding to one piezoelectric element may affect the amount of deformation of a vibration region neighboring to the certain vibration region. This type of case may also be termed the structural cross-talk phenomenon